The present invention relates in general to the process of reactivating spent clay. More particularly, the present invention relates to the process of reactivating spent clay used in the refining of oil or the re-refining of used motor oil or used vegetable oils.
In the refining and re-refining of used oil it is known that about 5 to 25% by weight of clay is used per weight of used oil. The used oil is typically re-refined using an acid-clay process. In this process, the clay is used to adsorb colored particles that keep the oil dark after it is subjected to the acidification step. The clay is also used to deodorize the oil. After use, the clay's color turns from its original white to a dark color. Further, the spent clay contains about 15% oil. The spent clay is considered toxic by the Environmental Protection Agency since the heavy metals in used oil are toxic. Any material containing more than 3% used oil is considered toxic and must be disposed of using expensive procedures. Since clay is also expensive and large amounts of it are used in the acid-clay re-refining process, it is desirable to recover the clay and re-activate it to a state where it is efficient in adsorbing carbonaceous materials and other particles that color oil and cause odors. This cuts down on the expense of clay purchase and reduces the cost and inconvenience of disposal of spent clay. This also reduces damage to the environment.
The usual method of disposing of spent clay is through landfill. However, since the spent clay still contains entrained oil in the amount of about 0.20 kg to about one (1) kg of oil per kilogram of dry spent clay, and said spent clay might ignite when disposed thereby. This possibility of fire poses an additional great danger to the environment and to the community in which the landfill is located over and above the possibility of pollution of ground waters from heavy metals in the entrained used oil leaching into the ground water.
Spent clay in order to be environmentally friendly must have an entrained oil of less than 3% by weight according to the regulations of the United States Environmental Protection Agency (EPA). Before this invention, that level of entrained oil was impossible to attain with the very best and most efficient separation method such as filtration or centrifugation.
In order to solve the problem of disposal of the spent clay, the best prior art solution offered to date has been to regenerate/reactivate and recycle the spent clay. The prior art discloses a number of methods to accomplish this. One method used to attempt to reactivate spent clay is solvent extraction. In this process, solvents such as toluene, xylene, benzene or other aromatic solvents, or ketones such as methyl ethyl ketone or acetone or aliphatic solvents such as hexane, heptane etc are mixed with the spent clay. The solvent extracts much of the entrained oil, but nobody really how how much of the carbon and pigment adsorbed colored particles are removed from the pores of the clay because these are not organic materials. The recovered clay from this process only has an efficiency in adsorbing colored particles of about 50% or less.
Another prior art process for reactivating spent clay is a heating method. In this method, the spent clay is heated above the cracking temperature of the entrained oil. This essentially boils off much of the entrained oil and essentially wastes this oil. It is unknown how much of the adsorbed particles such as carbon and pigments that this prior art method removes, and, in fact, the inventor believes this prior art method is ineffective in reactivating the clay because it turns much of the carbonaceous material entrained in the clay into coal or coke thereby failing to clear the pores of the clay and perhaps plugging up the pores even worse. Clay processed according to this process usually has an efficiency for adsorbing colored particles about the same as clay processed with solvent extraction only.
Another example of a prior art clay reactivation process is taught in U.S. Pat. No. 5,538,915. This patent teaches a four step process of (1) solvent extraction using about 250 cc of solvent per 10-15 grams of clay (2) oxidation by subjecting the clay to temperatures in the range of 80-90.degree. C.; (3) acidification of the re-refined oil with hydrochloric or sulfuric acid; and (4) neutralization of the pH of the clay. This process has been found by experiments of the inventor to not work well or at all in reactivating the clay and lightening the color of the clay back to it virgin color and virgin adsorption efficiency.
To date none of the prior art processes has been proven to result in regenerated clay which may be re-used a high a number of times and having almost the same efficiency as virgin clay to lighten the color and deodorize re-refined oil from an acid-clay process. Thus, even after using the prior art methods, the spent clay still has to be disposed off in a landfill after only one or two reactivations because of the low efficiency of the re-activated clay.